Goalkeeper Dario Sala made four saves for FC Dallas (5-3-1), which leads the Western Conference by four points over Colorado.
RSL (0-3-4) is winless after eight games and remains last in the West with only four points.
FC Dallas next plays at Chivas USA on May 26, while RSL is at Chicago on May 27.
Selena Gomez drops F-bomb, walks off stage during Jingle Ball performance
'SNL': 'Anchorman 2' cast, One Direction sing 'Afternoon Delight' [VIDEO]